1. Field of the Invention
The present invention relates to a method of adjusting the wafer processing sequence, and specially to a method of adjusting the wafer processing sequence for semiconductor manufacture.
2. Description of Related Art
In semiconductor manufacturing, each lot of wafers (hereinafter referred as to “lot”) needs to be subjected to multiple processes through a plurality of machines. In favor of semiconductor producers' profit, reducing production time and increasing productivity are the endeavors the semiconductor producers have been pursuing.
One of the key factors affecting the production time is the time for changing the process recipe. The machine needs to change its process recipe because of different designs of wafers. For example, the machine needs to adjust the processing parameters or replace modules for changing the process recipe. Therein, while the machine is changing the process recipe, the processing of wafers stops. Therefore, the longer the time needed for changing the process recipe, the longer it needs to finish the manufacturing of wafers. Some machines take less time to finish the change of process recipe. However, others, such as a photolithography machine, take much longer to do so.
When the photolithography machine processes a first lot, it uses a first mask. Before proceeding the processing of a second lot with different process recipe, the first mask needs to be moved out and then a second mask need to be moved in. The replacement of the masks takes time; therefore the total production time for the second lot becomes longer.
The other key factor is the time the machine waits for the next lot, even though the process recipes for the previous lot and the next lot are the same. Since the machine is a batch-type machine, the machine starts to operate only when a predetermined amount of lots with the same process recipe are inside the machine. For example, if the determined amount of lots is 4, the furnace tool starts to operate as soon as all four lots are inside the furnace tool. If the amount of lots has not reached the determined amount, then the machine does not work until the rest amount of lots has been supplied, which would lead to longer time for completing the manufacturing of wafers.
In the view of above, if a process engineer fails to put those lots with the same recipe together when arranging the processing procedure, the time needed to finish the manufacture of wafers unavoidably increases.
Therefore, there is a need for an improved method that overcomes the above disadvantages.